Figuring out if an antiretroviral drug regimen is not working properly can be determined in three ways:
A detectable or increasing viral load does not necessarily mean that drug-resistance mutations have occurred. A detectable viral load may be due to poor adherence or poor absorption. While these can eventually lead to the emergence of drug-resistance mutations, viral load can become detectable before they develop. Thus, it is important to act quickly and determine the reason why viral load is increasing soon after it becomes detectable.
If resistance mutations have developed, viral load tests cannot determine whether or not the virus is resistant to one specific drug or the entire regimen. Moreover, in a person with drug-resistant HIV, viral load testing cannot determine which drug or combination of drugs is likely to be the most effective in the future.
To look for drug resistance, there are two tests, or assays, available to people living with HIV and their healthcare providers. The first is called genotypic testing. Genotypic tests can help determine whether specific mutations are causing drug resistance and drug failure. The second method, called phenotypic testing, is a more direct measure of resistance and, more specifically, of the sensitivity of a person's HIV to particular antiretroviral drugs.